[gardening] Marking ListBase_class_A01_t03 as Slow.

Similar to the changes made in 78482496d50.

Change-Id: Iebaf87506bad7ed3927b52fef9134c514edafc7c
Reviewed-on: https://dart-review.googlesource.com/c/88576
Reviewed-by: Stevie Strickland <sstrickl@google.com>
Commit-Queue: Stevie Strickland <sstrickl@google.com>
diff --git a/tests/co19_2/co19_2-kernel.status b/tests/co19_2/co19_2-kernel.status
index f90927f..10ad9d2 100644
--- a/tests/co19_2/co19_2-kernel.status
+++ b/tests/co19_2/co19_2-kernel.status
@@ -478,6 +478,7 @@
 
 [ $runtime == vm && $system == macos && ($compiler == dartk || $compiler == dartkb) ]
 LibTest/collection/ListBase/ListBase_class_A01_t02: Pass, Slow
+LibTest/collection/ListBase/ListBase_class_A01_t03: Pass, Slow
 LibTest/collection/ListMixin/ListMixin_class_A01_t02: Pass, Slow
 LibTest/collection/ListMixin/ListMixin_class_A01_t03: Pass, Slow
 LibTest/core/List/List_class_A01_t02: Pass, Slow